A control valve for the application of a desired pressure in a work circuit, having a pressure chamber connected with a pressure source, a control chamber separated during the rest position of the valve from the pressure chamber by a first seat valve and connected to the work circuit and also connected to a pressureless connection during the rest position of the valve, and finally the control valve having an activating piston, by means of which, when the control valve is operated, first the connection between the control chamber and the pressureless connection is interrupted and then the first seat valve is opened.
Such a control valve is, for instance, known from German Offenlegungsschrift No. 25 31 264, FIG. 1 (reference numerals 9-17). There is a part of a main brake cylinder for dual-circuit brakes and serves to apply brake pressure to a brake circuit. Such brake systems are also called full power systems.
Control valves of the kind described above are also called proportional valves. They can be used, besides control of brake pressure, in other fields, as for instance as control valves for the regulation of levels or in power steering in motor vehicles.
Such control valves have the advantage over control valves developed as pure slide valves in that leakage is less and less demand is made on precision in manufacturing, however they show the so-called opening jump when the seat valve, which is under pressure only on one side from the pressure source, is opened.